This preprint presents a novel, membrane-free, and chemical-free domestic water softening framework integrating Zinc-Doped Template-Assisted Crystallization (TAC) with a 20 mm Rietema micro-hydrocyclone. The system thermodynamically promotes the precipitation of dissolved calcium (Ca2+) and magnesium (Mg2+) ions into 2 to 5 micrometer aragonite crystals, which are subsequently separated via centrifugal acceleration under standard domestic network pressures (2.5 bar). Numerical modeling and hydrodynamic simulations demonstrate a net hardness removal efficiency of approximately 79%, a reduced wastewater split ratio below 10%, and an ultra-low specific energy consumption (approximately 0.056 kWh/m3), offering a scalable and low-waste alternative to conventional reverse osmosis systems. W